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<title>lwres_noop</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="id2476275"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>lwres_nooprequest_render, lwres_noopresponse_render, lwres_nooprequest_parse, lwres_noopresponse_parse, lwres_noopresponse_free, lwres_nooprequest_free &#8212; lightweight resolver no-op message handling</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">
#include &lt;lwres/lwres.h&gt;</pre>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_nooprequest_render</b>(</code></td>
<td>lwres_context_t *�</td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_nooprequest_t *�</td>
<td>
<var class="pdparam">req</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_lwpacket_t *�</td>
<td>
<var class="pdparam">pkt</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_noopresponse_render</b>(</code></td>
<td>lwres_context_t *�</td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_noopresponse_t *�</td>
<td>
<var class="pdparam">req</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_lwpacket_t *�</td>
<td>
<var class="pdparam">pkt</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_nooprequest_parse</b>(</code></td>
<td>lwres_context_t *�</td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_lwpacket_t *�</td>
<td>
<var class="pdparam">pkt</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_nooprequest_t **�</td>
<td>
<var class="pdparam">structp</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
lwres_result_t
<b class="fsfunc">lwres_noopresponse_parse</b>(</code></td>
<td>lwres_context_t *�</td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_lwpacket_t *�</td>
<td>
<var class="pdparam">pkt</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_noopresponse_t **�</td>
<td>
<var class="pdparam">structp</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_noopresponse_free</b>(</code></td>
<td>lwres_context_t *�</td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_noopresponse_t **�</td>
<td>
<var class="pdparam">structp</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_nooprequest_free</b>(</code></td>
<td>lwres_context_t *�</td>
<td>
<var class="pdparam">ctx</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_nooprequest_t **�</td>
<td>
<var class="pdparam">structp</var><code>)</code>;</td>
</tr>
</table>
</div>
</div>
<div class="refsect1" lang="en">
<a name="id2543522"></a><h2>DESCRIPTION</h2>
<p>
      These are low-level routines for creating and parsing
      lightweight resolver no-op request and response messages.
    </p>
<p>
      The no-op message is analogous to a <span><strong class="command">ping</strong></span>
      packet:
      a packet is sent to the resolver daemon and is simply echoed back.
      The opcode is intended to allow a client to determine if the server is
      operational or not.
    </p>
<p>
      There are four main functions for the no-op opcode.
      One render function converts a no-op request structure &#8212;
      <span class="type">lwres_nooprequest_t</span> &#8212;
      to the lighweight resolver's canonical format.
      It is complemented by a parse function that converts a packet in this
      canonical format to a no-op request structure.
      Another render function converts the no-op response structure &#8212;
      <span class="type">lwres_noopresponse_t</span>
      to the canonical format.
      This is complemented by a parse function which converts a packet in
      canonical format to a no-op response structure.
    </p>
<p>
      These structures are defined in
      <code class="filename">lwres/lwres.h</code>.

      They are shown below.
    </p>
<pre class="programlisting">
#define LWRES_OPCODE_NOOP       0x00000000U
</pre>
<p>
    </p>
<pre class="programlisting">
typedef struct {
        lwres_uint16_t  datalength;
        unsigned char   *data;
} lwres_nooprequest_t;
</pre>
<p>
    </p>
<pre class="programlisting">
typedef struct {
        lwres_uint16_t  datalength;
        unsigned char   *data;
} lwres_noopresponse_t;
</pre>
<p>
    </p>
<p>
      Although the structures have different types, they are identical.
      This is because the no-op opcode simply echos whatever data was sent:
      the response is therefore identical to the request.
    </p>
<p><code class="function">lwres_nooprequest_render()</code>
      uses resolver context <em class="parameter"><code>ctx</code></em> to convert
      no-op request structure <em class="parameter"><code>req</code></em> to canonical
      format.  The packet header structure <em class="parameter"><code>pkt</code></em>
      is initialised and transferred to buffer
      <em class="parameter"><code>b</code></em>.  The contents of
      <em class="parameter"><code>*req</code></em> are then appended to the buffer in
      canonical format.
      <code class="function">lwres_noopresponse_render()</code> performs the
      same task, except it converts a no-op response structure
      <span class="type">lwres_noopresponse_t</span> to the lightweight resolver's
      canonical format.
    </p>
<p><code class="function">lwres_nooprequest_parse()</code>
      uses context <em class="parameter"><code>ctx</code></em> to convert the contents
      of packet <em class="parameter"><code>pkt</code></em> to a
      <span class="type">lwres_nooprequest_t</span> structure.  Buffer
      <em class="parameter"><code>b</code></em> provides space to be used for storing
      this structure.  When the function succeeds, the resulting
      <span class="type">lwres_nooprequest_t</span> is made available through
      <em class="parameter"><code>*structp</code></em>.
      <code class="function">lwres_noopresponse_parse()</code> offers the same
      semantics as <code class="function">lwres_nooprequest_parse()</code>
      except it yields a <span class="type">lwres_noopresponse_t</span> structure.
    </p>
<p><code class="function">lwres_noopresponse_free()</code>
      and <code class="function">lwres_nooprequest_free()</code> release the
      memory in resolver context <em class="parameter"><code>ctx</code></em> that was
      allocated to the <span class="type">lwres_noopresponse_t</span> or
      <span class="type">lwres_nooprequest_t</span> structures referenced via
      <em class="parameter"><code>structp</code></em>.
    </p>
</div>
<div class="refsect1" lang="en">
<a name="id2543672"></a><h2>RETURN VALUES</h2>
<p>
      The no-op opcode functions
      <code class="function">lwres_nooprequest_render()</code>,

      <code class="function">lwres_noopresponse_render()</code>
      <code class="function">lwres_nooprequest_parse()</code>
      and
      <code class="function">lwres_noopresponse_parse()</code>
      all return
      <span class="errorcode">LWRES_R_SUCCESS</span>
      on success.
      They return
      <span class="errorcode">LWRES_R_NOMEMORY</span>
      if memory allocation fails.
      <span class="errorcode">LWRES_R_UNEXPECTEDEND</span>
      is returned if the available space in the buffer
      <em class="parameter"><code>b</code></em>
      is too small to accommodate the packet header or the
      <span class="type">lwres_nooprequest_t</span>
      and
      <span class="type">lwres_noopresponse_t</span>
      structures.
      <code class="function">lwres_nooprequest_parse()</code>
      and
      <code class="function">lwres_noopresponse_parse()</code>
      will return
      <span class="errorcode">LWRES_R_UNEXPECTEDEND</span>
      if the buffer is not empty after decoding the received packet.
      These functions will return
      <span class="errorcode">LWRES_R_FAILURE</span>
      if
      <code class="constant">pktflags</code>
      in the packet header structure
      <span class="type">lwres_lwpacket_t</span>
      indicate that the packet is not a response to an earlier query.
    </p>
</div>
<div class="refsect1" lang="en">
<a name="id2543738"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">lwres_packet</span>(3)</span>
    </p>
</div>
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